Simultaneously achieve high output and low cost
The range of applications for LEDs is expanding from signal displays to a wide range of markets including LCD panel backlighting and lighting. A key factor in expanding applications is the ever-decreasing price, while many technologies offer cost-effective LED packages for display applications. In general, this area can be distinguished by lower component costs and lower cost manufacturing processes.
Extended life plastic
In applications such as LCD panel backlighting and illumination, LEDs that output more than 1W are often used. The heat generated by these high-output LEDs not only reduces the luminous efficiency, but also reduces the quality of the packaging material itself. Therefore, the key now is to solve these problems and reduce the cost of packaging.
Japan's Panasonic Electric Works has developed a plastic substrate and heat sink that can improve radiation performance (Figure 8). Metal substrates such as aluminum, while providing higher radiation performance, are relatively more expensive. As a result, the company abandoned metal and tried to extend its service life by improving the thermal radiation properties of plastic substrates. Panasonic Electric Works improved the process of adding filler to the plastic layer in two layers of copper, increasing the thermal conductivity of the substrate from 1 W/mK to 2 W/mK or 3 W/mK. The company explained that the thermal radiation performance of plastic substrates is currently not comparable to aluminum, but the company will continue to develop commercial products with thermal conductivity of 2W/mK to 3W/mK, and will further improve thermal conductivity.
Reduce the cost of packaging components.
Panasonic Electric Works extends the life of plastic substrates by improving the thermal radiation properties of plastic substrates and the resistance of plastic materials to heat and light. TDK-EPC's varistor substrate protects LEDs with large output power from electrostatic discharge without the use of Zener diodes.
At the same time, Japan's Risho Kogyo proposed to convert epoxy to silicon to increase the use of plastic in LED package substrates. The company said that when exposed to light, heat and other environments, the life of epoxy resin is only a few thousand hours, relatively short. At the same time, there is growing interest in ceramic materials that can provide tens of thousands of hours of life, but ceramics tend to be more expensive than plastics. According to the company, the new plastic substrate using silicon only needs "a small part of the cost of ceramics, but it can provide the same service life." The company expects to provide samples in the first half of 2010.
Japan's TDK-EPC Corporation has proposed a method to reduce the number of components in LED packaging. A high output power LED typically contains a Zener diode to protect the device from electrostatic charge generated during the packaging process. TDK-EPC recommends the use of zinc oxide (ZnO) varistors instead of the commonly used alumina (Al2O3) submounts. Even in the absence of a Zener diode, this varistor can discharge charge and withstand electrostatic discharges of up to 12kV. TDK-EPC is currently sampling new varistor substrates and plans to commercialize them by the end of 2010.
Solve problems with plastic packaging
Kyocera Chemicals has developed a plastic that is said to reduce processing costs and can be used in mass production applications such as compression molding (Figure 9). The company did not disclose detailed material information, only a thermoset plastic. Generally, silicon plastic used in an LED package has poor bonding force and has silver plating for reflection, which makes it unsuitable for compression molding. In addition, soft materials tend to cause distortion of the wires after encapsulation, and the products generally have excessive gas permeability, which tends to deteriorate the silver plating.
Reduce packaging process costs
Kyocera Chemical's packaging materials can be used in batch manufacturing, such as compression molding. DISCO has proposed a way to make thin sapphire substrates easier to handle. Canon Machinery has demonstrated a die bonder designed specifically for LEDs.
Newly developed plastics solve these silicone problems. The bonding strength with silver plating is dozens of times that of silicon plastic, and the hardness is 2 to 3 times. Its permeability factor is below 100. Kyocera Chemical said that the company's mass production target price will be lower than silica gel. The customer is currently evaluating.
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